Patent GB-837608-A (GB)
Title: Improvements in or relating to nuclear reactors
Inventor: MITCHELL KEITH JAMES
IPC: G21C1/12
Filed: 1956-09-27
Abstract: 837,608. Nuclear reactors. GENERAL ELECTRIC CO. Ltd. Sept. 26, 1957 [Sept. 27, 1956]. No. 29606/56. Class 39(4). A reactor core comprises units of moderating material assembled into a file and resting on a support having a higher coefficient of thermal expansion, the units being arranged in vertical columns held together at the top but free to move radially outward at the bottom with the support. In the central part of the pile 3 the brick layers are separated by two layers of tiles 2, one layer abutting in one lateral direction corresponding to the grain of the graphite, the other layer abutting in a direction at right angles to the first layer. The bricks 1rc outside the vertical line 4 form a neutron reflector and reflector layers 1rl are also provided at the top and bottom of the pile. The bricks and tiles are of square cross-section -and their abutting upper and lower surfaces mate with one another in the manner disclosed in Specification 813,547. The grain direction in the graphite bricks 1 is vertical and the bricks in adjacent columns are spaced from one another to allow for Wigner growth. To form a rigid cap at the top of the pile where the Wigner growth is less the top two pairs of tile layers are machined to be contiguous in both rectangular directions at once and have their grain vertical ; also the bricks of the top reflector layer are machined to be contiguous. Each brick or tile of a column has a central bore to form a continuous duct for the passage of coolant gas and the reception of fuel elements. The pile is supported on steel plates 6 laid on a grid 7, each column being located by a spigot 9 loosely fitting a plate 6 and entering the bore in the lower brick 8 of the column, Fig. 7. The pile forms a twentyeight sided polygon, Fig. 2 (not shown), and the two top layers are rigidly held together by four circumferential garter-type restraints 11 having the same coefficient of thermal expansion as the graphite. The restraints 11 comprise members hinged at 12 to each other and to members 13 or 16 embracing the pile corners A. A restraint 14 having a higher coefficient of thermal expansion and forming a parallel linkage with the restraint 11 is provided to support the pile cap in the event of failure of the restraint 11. To prevent twisting of the pile cap the restraints 16 have extensions 17, Fig. 5, with an end piece 18 locating between buffers 19 attached through brackets 20, 21 to the reactor shell 5. The remaining layers of the pile are merely located at the corners by restraints 13a so that the columns may move -with the expansion of the plates 6, these restraints being pivotally connected to vertical channels 22 by links 23, the upper ends of the channels being connected through links 23 to restraints 16. The channels 22 are tied together in pairs by strutting 25 and their lower ends 28 are pivotally connected to an annular extension 29 of the base 6. To prevent gas leakage between the base 6 and the pile an annular U-section stainless steel member is provided at the foot of the pile and tends to open up against the pile by the gas pressure to provide a seal, Fig. 8 (not shown).